As Perl evolves,
new desirable features get added.
The best ones seem to break backward compatibility,
unfortunately.
As a favor to downstream developers,
it's good to state explicitly which Perl version will not be able to parse your code.

For example,
the our keyword was first appeared in a stable Perl in version 5.6.0.
Therefore,
if your code employs our,
then you should have a line like this near the very top of your file:

use 5.006;

or

use v5.6.0;

The former is preferred as the latter can trigger v-string compatibility warnings. (If someone could please explain that to me, I'd really appreciate it!)

Additionally, it's good form to state that minimum version in your Makefile.PL or Build.PL file.